So here is a doozy, please post if you can share some helpful info as I work through this issue. 2002 X5 4.6is. Yesterday I went through and did a lot of maintenance that I'd been putting off. Installed all new:

L+R Front CV axles
L+R Front brake rotors & pads
L+R Front engine mounts
Front driveshaft flex-disk
Front differential fluid exchange
A/C Compressor replaced, system vac'd and charged.

Now.... After a couple of very brief driving cycles to bed the brakes and check my work, the car suddenly went into Trans Prog Failsafe and I hooked up BMW ISTA to see whats up. Immediately I noticed that the software would not "identify" the car- no communication to various modules. I manually entered the VIN and looked at the control tree and cleared all of the codes including the no-communication codes. All was OK for three more driving cycles into this morning when my wife and I went out for our Saturday morning coffee.

Same issue crops up with TRANS PROG FAILSAFE, and now no matter what I do I cannot get any communication with ANY module in the car, and clearing the codes results in the ISTA software immediately returning unable to communicate.

I find it extremely suspicious that this may be simply coincidental to the maintenance I did to the front, so am tempted to rule out a faulty module. Something I did must be causing a CAN BUS failure. Maybe I damaged a wire when lifting up the engine to replace the mounts?

Symptoms:
Engine starts/runs fine, with CEL for CAN timeout codes.
DSC/ABS Light immediately on start/run
Trans Prog Failsafe soon after engine start.
Instrument cluster's Tach/Oil temp/Water Temp/MPH gauges are inactive
Cannot communicate with any modules through ISTA or other stand alone scanners

Attempted Fixes:
Checked all fuses and relays. All OK.
All systems within the car seem to function normally.
OBDII port seems to be functioning with 12v present- ISTA will identify chassis type/prod date.
Alternator output shows 14.1-14-3v when idling. Batt at appr 13v when engine off.


Is there a relay or fuse in a hidden location that controls CAN communication? It is strange that I was able to reset the modules last night but not this morning.

Please post your thoughts!